[PATCH v10 08/12] fprobe: Add exit_handler support

Masami Hiramatsu
2022-03-08T11:10:17Z

Add exit_handler to fprobe. fprobe + rethook allows us to hook the kernel
function return. The rethook will be enabled only if the
fprobe::exit_handler is set.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
Changes in v10:
- Call rethook_hook() with mcount context flag.
Changes in v7:
- Fix unregister_fprobe() to ensure the rethook handlers are
finished when it returns.
- Update Kconfig help.
Changes in v6:
- Update according to the fprobe update.
Changes in v5:
- Add dependency for HAVE_RETHOOK.
Changes in v4:
- Check fprobe is disabled in the exit handler.
Changes in v3:
- Make sure to clear rethook->data before free.
- Handler checks the data is not NULL.
- Free rethook only if the rethook is using.
---
include/linux/fprobe.h | 6 ++
kernel/trace/Kconfig | 9 ++--
kernel/trace/fprobe.c | 116 ++++++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 122 insertions(+), 9 deletions(-)

diff --git a/include/linux/fprobe.h b/include/linux/fprobe.h
index 2ba099aff041..8eefec2b485e 100644
--- a/include/linux/fprobe.h
+++ b/include/linux/fprobe.h
@@ -5,13 +5,16 @@

#include <linux/compiler.h>
#include <linux/ftrace.h>
+#include <linux/rethook.h>

/**
* struct fprobe - ftrace based probe.
* @ops: The ftrace_ops.
* @nmissed: The counter for missing events.
* @flags: The status flag.
+ * @rethook: The rethook data structure. (internal data)
* @entry_handler: The callback function for function entry.
+ * @exit_handler: The callback function for function exit.
*/
struct fprobe {
#ifdef CONFIG_FUNCTION_TRACER
@@ -25,7 +28,10 @@ struct fprobe {
#endif
unsigned long nmissed;
unsigned int flags;
+ struct rethook *rethook;
+
void (*entry_handler)(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs);
+ void (*exit_handler)(struct fprobe *fp, unsigned long entry_ip, struct pt_regs *regs);
};

#define FPROBE_FL_DISABLED 1
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index e75504e42ab8..99dd4ca63d68 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -251,11 +251,14 @@ config FPROBE
bool "Kernel Function Probe (fprobe)"
depends on FUNCTION_TRACER
depends on DYNAMIC_FTRACE_WITH_REGS
+ depends on HAVE_RETHOOK
+ select RETHOOK
default n
help
- This option enables kernel function probe (fprobe) based on ftrace,
- which is similar to kprobes, but probes only for kernel function
- entries and it can probe multiple functions by one fprobe.
+ This option enables kernel function probe (fprobe) based on ftrace.
+ The fprobe is similar to kprobes, but probes only for kernel function
+ entries and exits. This also can probe multiple functions by one
+ fprobe.

If unsure, say N.

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 7e8ceee339a0..38073632bfe4 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -8,12 +8,22 @@
#include <linux/fprobe.h>
#include <linux/kallsyms.h>
#include <linux/kprobes.h>
+#include <linux/rethook.h>
#include <linux/slab.h>
#include <linux/sort.h>

+#include "trace.h"
+
+struct fprobe_rethook_node {
+ struct rethook_node node;
+ unsigned long entry_ip;
+};
+
static void fprobe_handler(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *ops, struct ftrace_regs *fregs)
{
+ struct fprobe_rethook_node *fpr;
+ struct rethook_node *rh;
struct fprobe *fp;
int bit;

@@ -30,10 +40,37 @@ static void fprobe_handler(unsigned long ip, unsigned long parent_ip,
if (fp->entry_handler)
fp->entry_handler(fp, ip, ftrace_get_regs(fregs));

+ if (fp->exit_handler) {
+ rh = rethook_try_get(fp->rethook);
+ if (!rh) {
+ fp->nmissed++;
+ goto out;
+ }
+ fpr = container_of(rh, struct fprobe_rethook_node, node);
+ fpr->entry_ip = ip;
+ rethook_hook(rh, ftrace_get_regs(fregs), true);
+ }
+
+out:
ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(fprobe_handler);

+static void fprobe_exit_handler(struct rethook_node *rh, void *data,
+ struct pt_regs *regs)
+{
+ struct fprobe *fp = (struct fprobe *)data;
+ struct fprobe_rethook_node *fpr;
+
+ if (!fp || fprobe_disabled(fp))
+ return;
+
+ fpr = container_of(rh, struct fprobe_rethook_node, node);
+
+ fp->exit_handler(fp, fpr->entry_ip, regs);
+}
+NOKPROBE_SYMBOL(fprobe_exit_handler);
+
/* Convert ftrace location address from symbols */
static unsigned long *get_ftrace_locations(const char **syms, int num)
{
@@ -77,6 +114,48 @@ static void fprobe_init(struct fprobe *fp)
fp->ops.flags |= FTRACE_OPS_FL_SAVE_REGS;
}

+static int fprobe_init_rethook(struct fprobe *fp, int num)
+{
+ int i, size;
+
+ if (num < 0)
+ return -EINVAL;
+
+ if (!fp->exit_handler) {
+ fp->rethook = NULL;
+ return 0;
+ }
+
+ /* Initialize rethook if needed */
+ size = num * num_possible_cpus() * 2;
+ if (size < 0)
+ return -E2BIG;
+
+ fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
+ for (i = 0; i < size; i++) {
+ struct rethook_node *node;
+
+ node = kzalloc(sizeof(struct fprobe_rethook_node), GFP_KERNEL);
+ if (!node) {
+ rethook_free(fp->rethook);
+ fp->rethook = NULL;
+ return -ENOMEM;
+ }
+ rethook_add_node(fp->rethook, node);
+ }
+ return 0;
+}
+
+static void fprobe_fail_cleanup(struct fprobe *fp)
+{
+ if (fp->rethook) {
+ /* Don't need to cleanup rethook->handler because this is not used. */
+ rethook_free(fp->rethook);
+ fp->rethook = NULL;
+ }
+ ftrace_free_filter(&fp->ops);
+}
+
/**
* register_fprobe() - Register fprobe to ftrace by pattern.
* @fp: A fprobe data structure to be registered.
@@ -90,6 +169,7 @@ static void fprobe_init(struct fprobe *fp)
*/
int register_fprobe(struct fprobe *fp, const char *filter, const char *notfilter)
{
+ struct ftrace_hash *hash;
unsigned char *str;
int ret, len;

@@ -114,10 +194,21 @@ int register_fprobe(struct fprobe *fp, const char *filter, const char *notfilter
goto out;
}

- ret = register_ftrace_function(&fp->ops);
+ /* TODO:
+ * correctly calculate the total number of filtered symbols
+ * from both filter and notfilter.
+ */
+ hash = fp->ops.local_hash.filter_hash;
+ if (WARN_ON_ONCE(!hash))
+ goto out;
+
+ ret = fprobe_init_rethook(fp, (int)hash->count);
+ if (!ret)
+ ret = register_ftrace_function(&fp->ops);
+
out:
if (ret)
- ftrace_free_filter(&fp->ops);
+ fprobe_fail_cleanup(fp);
return ret;
}
EXPORT_SYMBOL_GPL(register_fprobe);
@@ -145,12 +236,15 @@ int register_fprobe_ips(struct fprobe *fp, unsigned long *addrs, int num)
fprobe_init(fp);

ret = ftrace_set_filter_ips(&fp->ops, addrs, num, 0, 0);
+ if (ret)
+ return ret;
+
+ ret = fprobe_init_rethook(fp, num);
if (!ret)
ret = register_ftrace_function(&fp->ops);

if (ret)
- ftrace_free_filter(&fp->ops);
-
+ fprobe_fail_cleanup(fp);
return ret;
}
EXPORT_SYMBOL_GPL(register_fprobe_ips);
@@ -201,10 +295,20 @@ int unregister_fprobe(struct fprobe *fp)
if (!fp || fp->ops.func != fprobe_handler)
return -EINVAL;

+ /*
+ * rethook_free() starts disabling the rethook, but the rethook handlers
+ * may be running on other processors at this point. To make sure that all
+ * current running handlers are finished, call unregister_ftrace_function()
+ * after this.
+ */
+ if (fp->rethook)
+ rethook_free(fp->rethook);
+
ret = unregister_ftrace_function(&fp->ops);
+ if (ret < 0)
+ return ret;

- if (!ret)
- ftrace_free_filter(&fp->ops);
+ ftrace_free_filter(&fp->ops);

return ret;
}